The invention relates generally to the field of non-surgical treatment techniques and, in particular, to such techniques used for hyperthermia treatment of the prostate.
More particularly, the invention provides an improved energy-radiating instrument for intracavity use to heat body tissue selectively.
Prostatic disease, malignant or benign, is relatively common in men over 50 years of age. More than 90% of all men develop benign prostatic hyperplasia (BPH) by the eighth decade of life. It is the most common cause of urinary obstruction in men, and 10-20% of men will require prostatic surgery at some time in their lives to relieve obstructive symptoms. Presently, the treatment of choice for symptomatic BPH is surgery. That many patients suffering from BPH are elderly and may not be candidates for surgery, however, suggests that non-surgical alternatives for therapy warrant consideration.
Non-surgical treatments for BPH include medications such as alpha-adrenergic antagonists, 5-.alpha.reductase blockers, and hormones as well as mechanical dilatation. Recently, hyperthermia has been suggested as a possible treatment for BPH. Although the precise mechanism by which hyperthermia causes cell death is not fully understood, heat is known to disrupt both the cellular membrane and nuclear function. Although the biological rationale for non-surgically treating malignant tumors with hyperthermia is well established, clinical evidence has recently begun to suggest that hyperthermia may also be useful in the management of symptomatic (BPH). The anatomical location of the prostate permits various approaches to be used for treating localized prostatic disease with hyperthermia. Intracavity approaches to the prostate are possible through either the rectum or the urethra.
The transrectal approach is preferable for treating prostatic cancers because the rectum can accommodate a larger instrument which in turn can heat a larger volume of tissue. Other advantages to approaching the prostate through the rectum are that most prostatic cancers lie in the posterior portion of the prostate and are therefore most accessible transrectally. The urethra offers an easily accessible central location in the prostate for monitoring temperature. Most transrectal instrument designs feature water cooling to prevent damage to the rectal mucosa.
On the other hand, while transrectal hyperthermia instruments are advantageous for treating large prostatic lesions such as cancer, the transurethral approach has significant advantages for treating BPH. First, water-cooled transrectal instruments deliver a maximum temperature several millimeters beneath the rectal mucosa and in the posterior prostate, whereas transurethral microwave instruments deliver maximum temperature periurethrally and concentrate the hyperthermia around the symptomatic lesion. Secondly, transurethral instruments can be easily localized within the prostate using a balloon catheter and/or imaging techniques. This is more efficient than transrectal instruments which must be properly "aimed" at the prostatic lesion. Finally, the transurethral approach is less likely to cause complications resulting from damages to the rectal mucosa.
One problem facing known techniques for treating the prostate with hyperthermia is that the performance of known microwave radiating instruments, e.g. employing antennas, is a function of insertion depth. For optimum radiation, the antenna is to have antenna sections that are equal in length and that correspond to a quarter wavelength in the composite tissue/catheter medium. In typical practice, however, the length of one antenna section is dependent upon the depth to which the antenna is inserted into the patient. This insertion depth is determined by the clinical situation.
When insertion depth is not ideal based on theoretical calculations governing the operation of known transurethral microwave instruments, several problems are encountered. Antenna performance can be reduced due to increased reflected power at the antenna junction, which results in increased power requirements and ohmic heating of the antenna feedline. Clinically, this often results in pain for the patient, particularly at the entrance site of the catheter which the instrument employs to display the antenna sections. In severe situations, ohmic heating of the antenna feed-line can damage the patient's external sphincter making it difficult or impossible for the patient to voluntarily obstruct urine flow. Another problem is that as insertion depth is changed, the impedances presented by the antenna sections become unbalanced. This causes one antenna section to radiate preferentially, and displaces the heating pattern away from the desired pattern that occurs with balanced radiation.
It is, therefore, an object of the invention to provide a microwave hyperthermia instrument for intracavity use that radiates energy independently of insertion depth.
It is another object of the invention to provide such an instrument that limits the area over which energy is radiated.
It is still another object of the invention to provide such an apparatus that can be precisely positioned within a patient.
A further object is to provide a transurethral instrument having the foregoing features.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.